1. Field of the Invention
The application relates to a method utilized in a wireless communication system, and more particularly, to a method of handling a communication operation in a time-division duplexing (TDD) system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (COMP) transmissions/reception, uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Different from the LTE/LTE-A system operating in a frequency-division duplexing (FDD) mode (or simply FDD system), directions of subframes of a frequency band in the LTE/LTE-A system operating in a time-division duplexing (TDD) mode (or simply TDD system) may be different. That is, the subframes in the same frequency band are divided into UL subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
Please refer to FIG. 1 which is a table 10 of the UL/DL configuration with subframes and corresponding directions. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of directions for 10 subframes, respectively. In detail, “U” means that the subframe is a UL subframe where UL data is transmitted, and “D” means that the subframe is a DL subframe where DL data is transmitted. “S” means that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) is transmitted, and the special subframe can also be seen as the DL subframe in the present invention.
Furthermore, a UL/DL configuration of a legacy UE can be changed (i.e., reconfigured) according to system information (e.g., System Information Block Type 1 (SIB1)) transmitted by an eNB, e.g., from the UL/DL configuration 1 to the UL/DL configuration 3. A minimum periodicity of transmitting the SIB1 is usually large (e.g., 640 ms), and the legacy UE can only change the UL/DL configuration with the periodicity equal or greater than 640 ms. The semi-statics allocation cannot match fast varying traffic characteristics and environments, and there is space for improving system performance. Thus, changing the UL/DL configuration with a lower periodicity (e.g., lower than 640 ms) is considered.
However, when an advanced UE intends to change the UL/DL configuration fast (e.g., according to the traffic characteristics) or suffers from a fast change of the UL/DL configuration, the advanced UE may fail in the following situations. For example, the UE may miss a notification (e.g., DL control information (DCI)) for changing the UL/DL configuration. That is, the UE does not know the change of the UL/DL configuration. In another example, the UE may change the UL/DL configuration erroneously due to a false alarm. That is, the UE determines that the UL/DL configuration changes, while the UL/DL configuration does not. In another example, the UE may fail to transmit or receive a hybrid automatic repeat request (HARQ) feedback due to the change of the UL/DL configuration, i.e., HARQ discontinuity.
In addition, a DL HARQ process starts to operate, when the advanced UE cannot decode a received packet successfully. The advanced UE stores soft values of transmitted/retransmitted (by the eNB) packets in a soft buffer of the advanced UE, and combines the soft values to increase a probability of successful decoding, as known by those skilled in the art. The advanced UE continues the DL HARQ process until the packet is decoded correctly, or until a maximum number of retransmissions have been sent, at which time the DL HARQ process declares a failure and leaves it up to the DL HARQ process in radio link control (RLC) for trying again. However, the advanced UE should partition and use the soft buffer according to the UL/DL configuration of the advanced UE. In other words, the advanced UE may repartition the soft buffer, when the UL/DL configuration changes. Thus, frequent repartitioning of the soft buffer may happen, if the UL/DL configuration changes frequently. In this situation, the soft values may not be stored in the soft buffer correctly, e.g., the soft values may be overwritten, may not be stored due to insufficient number of partitions, etc.
Therefore, a method for solving the abovementioned problems is needed.